1. Field of the Invention
The present invention relates to torque converters and more particularly to a torque converter having increased vibration damping characteristics in many different operating states.
2. Description of the Related Art
A torque converter is known from DE 195 14 411 A1, wherein a torsional vibration damper is arranged in the connection path between the turbine wheel shell and the turbine wheel hub. A toothing at the shell engages with a counter-toothing at the hub, and provides a rotational play which limits the rotational angle for the torsional vibration damper formed by the engagement of the teeth with one another. Further, a lockup clutch is provided which, in order to transmit power, is coupled to the side of the torsional vibration damper that is also coupled with the turbine wheel shell. That is, the torsional vibration damper is active when the lockup clutch is in its disengaged state and the turbine wheel is rotatably driven during converter operation by work fluid conveyed in the turbine wheel as well as when the lockup clutch is engaged. The turbine wheel shell is therefore coupled with the housing so as to be fixed with respect to rotation relative to it. The operating states in which the torque converter is bridged or bypassed with respect to its converter function by the engagement of the lockup clutch, or in which the lockup clutch is disengaged and transmission of the output torque is accordingly generated by the torque converter, differ considerably with respect to the demands on the torsional vibration damper. In general, the lockup state or bypass state is an operation in which a vehicle drives at a relatively constant speed, that is, at a relatively constant rate of rotation of the internal combustion engine. Generally, in an operating state of this kind, only relatively slight torque variations occur. Thus, when the torsional vibration damper is designed too rigid, these occurring vibrations cannot be damped to the desired extent. However, in the non-bypassed state in which torque conversion occurs, a relatively large torque is transmitted to the converter output shaft by the turbine wheel. This torque must be transmitted through the torsional vibration damper, so that if the torsional vibration damper is designed too soft, it very quickly reaches its limit and can accordingly no longer provide a damping function. Thus, since this known torsional vibration damper works in the bypass state as well as in hydrodynamic operation, i.e., in the torque conversion state, it must, as a rule, have sufficient spring stiffness to prevent the torque converter from reaching its limit at least to a great extent, also in the torque conversion state. As a result, the desired decoupling of vibrations cannot be provided by the torsional vibration damper in the case of smaller transmitted torques or smaller torque variations.